


The Five Day Flu: Afterhours

by skerb



Category: Undertale (Video Game)
Genre: ( ͡° ͜ʖ ͡°), Alternate Universe - Undertail (Undertale), Ecto-Penis (Undertale), Established Relationship, Explicit Sexual Content, Fluff and Smut, Hand Jobs, Heavy Petting, Hickies, Idiots in Love, Love Bites, M/M, Making Out, Morning Sex, Overstimulation, Rough Sex, Sensitive bones, Sequel, Tender Sex, Undertale Monsters on the Surface, Vaginal Fingering, grillbussy, the five day flu
Language: English
Status: Completed
Published: 2020-07-28
Updated: 2020-07-28
Packaged: 2021-03-06 03:33:54
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,868
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25566730
Author URL: https://archiveofourown.org/users/skerb/pseuds/skerb
Summary: Sans and Grillby finally catch a break.
Relationships: Grillby/Sans (Undertale), Sansby
Comments: 19
Kudos: 88





	The Five Day Flu: Afterhours

**Author's Note:**

  * Inspired by [The Five Day Flu](https://archiveofourown.org/works/23635078) by [skerb](https://archiveofourown.org/users/skerb/pseuds/skerb). 



> A later continuation to my fic "[The Five Day Flu](https://archiveofourown.org/works/23635078)", where Sans forces himself to go without sex to resolve his heat.

Yeah, it’s been awhile.

Sans definitely missed this. He’s curled up in Grillby’s bed, in his suite next to the fire hall. Grillby’s next to him, tangled in sheets that smell like him, pressed into him as he takes his time to devour his mouth. Sans huffs out a breathless sound through his nasal aperture, grinning as his soul quickens, aches and longs for more of Grillby’s touch.

He touches back. His hand cups back behind Grillby’s head, tickling the flames that lick at his fingers. His taste is heady and warm, filling him up to his collarbones and trickling down his spine.

Sans can’t stop the sounds he makes. He’s waited so long for this. His body has barely been cooperating, stuck with the notion that if he’s given physical affection, he should cringe away. Grillby’s always good to him, so when Sans woke up in the morning feeling relatively ok, he pulled the fire monster close to steal a kiss.

It’s probably been close to an hour, casually coming up for air with secretive laughs and pleased hums. Sans only grinned when Grillby asked him how he was, answering him with another kiss.

The heat’s gone.

It’s slow. They have all the time in the world. His magic is thick and hot, but he ignores it as much as he can, focusing on the way his body unwinds with simple touches and how much Grillby’s voice leaves him unravelled. Covertly, he slings his leg around Grillby’s hip, moving closer until the fire monster is beneath him.

It’s so easy to be with him, Sans thinks. He’s lucky to have Grillby, patient as a saint and as indulgent as the devil. He grins up from beneath Sans, flushed in tonal hues of gold and soft peaches, thoroughly wrecked just from a little making out. Hungrily, Sans sighs and leans down again to resume their maddeningly slow pace.

This time, he inches back a little against the pleasant hardness under his tailbone. A little extra something to send Grillby a clear message. He receives it loud and clear, a startled noise deep in Grillby’s throat. Sans tries the angle again, moving his hips in a low curve. One of Grillby’s hands finds the flare of his ilium but it doesn’t move, watching for some sign for permission.

Sans decides to let Grillby wait a little. He’s patient. They’ve got all the time in the world. Sans’ legs tremble with that first wash of nerves when he sinks down a little more, situating his coccyx at the crux between Grillby’s thighs.

He just radiates heat, a warm and pleasurable temperature that’s nothing like the weather outside, nor the burgeoning ache that took Sans by a stranglehold just a couple of weeks before. It’s tender in a way that’s measured and sure, a pleasantness that reaches up Sans’ femurs with elegant, invisible fingers.

He sighs. “I missed this,” he whispers, still catching his breath even as he gives Grillby another tease by rolling his hips again. Grillby adjusts how he lays, sliding his feet up so his thighs create something to lean back on. It’s like a shockwave, intricate shivers that sneak up Sans’ back.

 _“Proactive?”_ Grillby observes, though there’s a slight catch to his voice when Sans moves against him. It’s not often that Sans takes initiative, so he tends to savour it when Sans wants to lead.

Sans hums low in his throat in affirmation. His tailbone’s sensitive, flushed beneath his shorts. He tries to sink down further, nestled deep in that spot. He thinks of Grillby’s former position, the way his thighs trembled when it came to be too much.

He’s being good. He’s taking his time. There’s no rush; they’ve got nowhere else to be. No commitments. No plans. Just themselves and a lazy morning, sharing each others’ breaths like they mean to fuse together into one being.

Sans leans down after the brief respite, moving his forearm over Grillby’s shoulder to capture another kiss. He’s learned from Grillby what he likes, and he can never get enough of how he tastes. Grillby’s hand moves up, thumbing his waistband, _asking_ to slip inside. Sans shakily exhales into the next kiss, amused. With the way pants are on him, Grillby need only to reach between his shirt and slacks, and, surprise, he’s there.

But no, he asks permission because his comfort is important to Grillby. That makes his soul skip a beat, Grillby’s dense heat radiating south as he reaches and teases down the length of his ischium. Sans shudders, his mouth going slack when Grillby laughs softly, nipping at his jaw.

 _“Antsy..?”_ Grillby asks, and Sans recalls the few conversations - post-heat - about how his brother had described him. He snerks to himself, then tries to cleanse his brain by laying his tongue against Grillby’s neck. It gives a satisfying sizzle when Sans pushes his magic against it, and the fire monster huffs out a startled noise. It’s his aim to distract Grillby from teasing him, no matter how much he tries.

His attention is somewhat diverted by the simple way Grillby thumbs at his ischium, teasing in slow, smooth circles. As he does, Sans moves his hips forward, catching Grillby’s fingers into the diffuse magic.

Sans aims to make the mark he’s working on a little bigger, pushing up Grillby’s throat. He can hear and feel Grillby’s flames rebuke him, glimmering, fluttering and wild. The fire monster’s breaths begin to quicken even as he chuckles.

 _“Mark me up,”_ he encourages, and Sans can feel the sentiment sink low into his pelvis. Yeah, he likes that idea. He’s definitely gonna do that. Grillby inhales long and deep when Sans teeths his neck just a little, motivating him. His hot fingers flirt with the void of his ischium, his other hand smoothing down the opposite side of his ribs. _“Go on.”_

Sans takes the suggestion, the words reverating in his soul like a plucked string. He’s slow and steady despite the wash of nerves. Pushing his free hand down to Grillby’s shoulder, he scrapes his bottom teeth against the fire monster’s nape just as he turns throat. The sound he makes has another shudder of unbridled want coursing through Sans’ body, warming him up. He answers it with a soft moan into Grillby’s throat, drunkenly moving back to inspect his work.

There’s a large patch three fingers wide, sizzling and hot. Grillby’s eyes are bright as Sans assesses him, though he tries not to yearn to Grillby’s touch too much. His breath is hot, tinged with fire magic. His mouth tastes like warm spices like the ones that permeate most holiday drinks this time of year.

“You’re sneaky,” Sans laughs softly. He half-hangs over Grillby’s body, nudged where the fire monster wants him with the firm yet soft hand on his back. He sinks down again, a little pop of pleasure guiding his hips as Grillby’s touch tickles against the top of his sacrum. “You always go for th.. the cheap shot.”

Grillby’s smirk is devilish. Sans laughs again, his expression changing imperceptibly when the tips of Grillby’s fingers inch higher, barely there. He drops a soft _“Oh,”_ but despite the firm grasp on his words, he just couldn’t hold it. Grillby appears extremely satisfied with the result.

_“Better? Or would you have me on top?”_

That speaks to Sans’ awakened libido like a freight train through a quiet night. He swallows hard, the words _have me_ ricocheting around his skull like charged atoms. As always, when Grillby is direct, Sans’ brain fumbles and his face flushes enough to put the sky to shame. Regardless, Grillby tends to relish it when he gets under Sans’ metaphorical skin.

“Uh,” Sans says, demonstrating how well his mind works under horny pressure. While it’s an appealing thought to have Grillby ride him through the mattress again, it also left him an overstimulated mess and he had back pain for literal weeks.

Carefully, he exhales the burst of pleasure when Grillby’s fingertips slowly circle his lowermost lumbar. “Unless… you wanted something else…” he murmurs softly, offering an alternative just in case Grillby had other ideas.

Grillby’s thumb rests at the top of his sacrum, slow, steady circles making Sans’ legs tremble. He’s careful, oh so careful to make sure that Sans really consents before going forward. Sans’ eyes are partially open, his face flushed and his breaths heavy. He could take a hint that Sans wants more of such delightful torture, but Grillby’s always needed confirmation.

_“More?”_

Sans sinks down lower, firming Grillby’s touch against his body. He huffs out an impatient noise, nods, then mutters, “Jeez, man. You don’t gotta make me beg every time.”

Grillby clicks his tongue as though in admonition, but lays the pads of his fingers onto Sans’ sacrum anyway. He delights in the shudder that wracks Sans’ body, his arms threatening to quake under the simple touch.

 _“That isn’t a yes…”_ Grillby chastises a little softly, though Sans can hear the tease in his voice even as he pushes his pelvis more against his hand. His magic mingles with the flames that come to visit him, ever-curious and explorative. They keep aside until Sans shakily nods, his breaths quickening. His body wants them, urging them to creep into the free spaces in his body like his magic can’t control it.

The flames come to him. They respond well to him, flickering between his joints like faerie lights and licking his sensitive bones. Sans makes a noise low in his throat. It’s locked there, but it’s definitely something in the affirmative. His tailbone throbs, the holes in his sacrum slowly blooming with warmth.

With no clear ‘yes’, Grillby knows better than to push. Sans yearns towards his hand, a silent invitation. He’s always been a shy boy when it comes to pleasure. Sans dips his head, a startled huff escaping him. Then belatedly, there it is.

“Please.”

His face scalds shamefully, but Grillby guides him down, cupping his shoulder as flames make him sensually warm, beckoning his hips to move. The warmth travels down from his shoulder and down each vertebrae, causing Sans to shake out surprised noises like it’s all new. As though he’s never felt it all before.

It’s been awhile. A few weeks into their third month without, and it feels fresh. Sans can’t help but squirm as a particularly bold flame gives a tentative lick to the tip of his coccyx. He pushes himself up, inching forward just a little so Grillby can still tease him. It feels like his magic is about to erupt.

He’s so warm. He doesn’t care about the sounds he makes, knowing Grillby is enthralled by them. He can’t help the broken, muffled gasp when the fire monster’s hand stirs along his magic, coaching it towards his pubic symphysis with the density of a dying sun.

And Grillby’s focus is on him, all of him. Sans is helpless under his gaze, trying not to come undone even as Grillby expertly unravels all the threads. Even as Grillby’s hand curls towards the inverse of his pubis, white-hot fingers aching in all the right ways, Sans whimpers.

Grillby’s eyes glitter mischievously. _“What will you give me?”_ sighs out of him, and Sans’ body responds eagerly. As the fire monster tugs at his waistband, Sans’ magic tightens to the point of discomfort, until he allows it to finally take shape.

Grillby is happy with anything he’s given, but Sans’ cock is something of a rare treat. When he submits, he’s usually ready with something more receptive, as he’s willing to accept Grillby into his body when he’s randy enough. Sans just watches Grillby, his teeth parted around fast pants as Grillby gives him a moment to adjust to his newly formed magic.

Above him, though, Sans takes initiative. He gets up to his knees, straddling Grillby’s hips, and eases down one side of his shorts in a tantalising tease. Grillby lights up for him, all pretty golds and soft ambers like the world’s best nightlight. Sans feels a little empowered by that, but he’s still shy. He still needs coaxing forward, for Grillby to urge him to continue.

Grillby’s gaze rakes over him, hungry and enamoured. It’s enough to make Sans tremble as he pushes his waistband down on one side, clumsily straddled while his cock bobs against the fabric, erect and eager. He swallows a strained laugh, his face scalding and flushed. Grillby’s free hand glides down his ribs to his hip, urging and gentle.

“How do you want it?” Amazing, he managed not to stammer. Sans doesn’t believe the words that spill out of his mouth, but Grillby looks endeared. He feels a firm tug at his right hip, the sharp snap of elastic against the flare of his ilium. Sans’ grin turns crooked. “Not through the shorts. Got it,” he jokes, and Grillby’s smirk bunches into a cheeky thing that has Sans’ soul thumping hard.

It takes some manoeuvring, but Sans manages to fold his leg over Grillby’s abdomen to tear his shorts off. He lets them drop unceremoniously off the side of the bed and nestles atop of his lover’s thighs.

He’s naked from the waist down, but Grillby’s still dressed. Well… more or less. He’s usually in something button-down, and he’s grown fond of comfortable sweatpants during the long autumn nights.

Grillby’s hands reach up to Sans’ chest, the span of his fingers splayed over his ribs. He almost covers them all, warming him through his shirt. Sans sighs against the touch, involuntarily moving forward as Grillby’s thumbs stroke him, careful and firm. It feels better now that he isn’t sweltering.

 _“Would like this… removed,”_ Grillby requests, his voice low.

Sans can feel how hot he’s gotten, barely contained enough to keep himself from singeing his clothes. The heat radiates down from Grillby’s hands to his cock, which adores the warmth. He sighs out, longing, and slinks his hands around Grillby’s wrists before he leans against his touch and pleads, “Burn it.”

Grillby makes an inquisitive sound, but it’s also strangled like he’s trying and failing to keep himself in check. Sans’ grin quirks shyly and he tries again.

“Burn it off me.”

With the low tone bordering on something filthy, Grillby’s flames get a little excited for permission. It’s ok, Sans wasn’t in love with this shirt, and he quite likes how Grillby’s affected by his tone of voice.

He huffs a startled breath as he always does when he feels Grillby amp up, sparks and embers drifting off his arms as he allows his flames to travel to Sans’ willing body.

Flames travel down Grillby’s arms, slowly igniting his shirt like glowing embers. Sans can feel Grillby’s eyes on him as his shirt is consumed by the flames, trailing up and around his hands like dry summer grass. It catches against his ribs, soft licks of flames gentle in their pursuit to render him completely bare.

By the end of it, the flames have nestled in tight to his chest, clinging to his bones. They ignite little bursts of sensation, glowing along the cracks and steaming out any moisture. His sweat is seared away and all Sans can feel is a heavy haze of heat as he exhales a plume of steam. Grillby looks, for the most part, extremely turned on.

“And here you have me,” Sans murmurs, though his thoughts derail when the residual flames slip down his spine. Grillby’s hands are warm and heavy against his ribs, holding him up, keeping him in place. He shudders, unable to help himself and the small “Ah-!” coaxed from his throat when an errant flame curls up inside of his pelvis.

He can feel it, nestled in a small spiral, gently twisting in throbbing movements. Sans is sure this is somehow revenge for something as the flame moves, coaxing him to jerk forward. The glide of his hips is smooth, a rolling motion that makes it feel like he’s getting fucked. He tries the movement again, sees the deeply pleased look in Grillby’s eyes as he keeps his hands on Sans’ ribs.

It feels good. It’s subtle in all the ways that fire caresses him, kisses him and makes him feel, but Sans can’t help the low noise he makes when the flame flirts with the lowermost foramen of his sacrum. Grillby thumbs his chest, the sensation like a livewire, making an unbidden shiver crawl up Sans’ spine.

His chuckle’s a little low, bashful and bare as he pushes his hips forward again with the movement. He knows he’s grinding down on the fire monster’s lower abdomen, the heat and controlled flare too telling under his ass. Grillby sends him one of his patented smouldering looks, slinking one of his hands down and taking Sans’ with it.

Sans almost bites his tongue when heat envelops around his member, guiding him to hold it there as Grillby slowly pumps him in time with his thrusts. It makes a gusty sigh escape Sans, his hand at Grillby’s wrist as though he’s not sure if he should keep it there or to pull it away. A slow knot coils somewhere at the centre of his being, ebbing and flowing like the tides.

Limber, Grillby bends up, sliding his hand behind Sans’ back. Silently obedient, Sans’ hand drops to the fire monster’s hip, feeling the firm heat under his tailbone as he slides forward into Grillby’s grip. He can feel Grillby’s thighs behind him but resists lying back against them, heavy and warm.

The sweet heat continues to climb. Unlike the ever-expanding ceiling above him when Grillby had healed him to climax before, pleasure ripples over the metaphorical windowsills and floods the dining room like water. It climbs higher, and Sans can’t keep his eyes off Grillby, flushed and biting back moans when he squeezes around his cock, teasing the tip, swirling so noises draw out of him like a magnet.

Sans’ hands shake, eager to be put to use. The hand at Grillby’s hip kneads incessantly with their pace, mapping out the shape of him. He’s not sure if Grillby’s taking a receptive role or not, or if they’ll enjoy each other as is. Regardless, Grillby’s leading him closer to the headboard, something to hang onto or something for Grillby to lean back against.

In all honesty, Sans is up for either, so long as they can chase pleasure together like this.

Sans whimpers on a noise, the flame in his hip box coaxing him to thrust a little faster. A little harder. It breaks out into a full moan as Grillby starts to twist his wrist with each stroke, and Sans’ grip tightens. He drops a strangled off swear, wrenching his face to the side like it’ll save him from losing it completely.

Yeah, he’s sure this is some kind of revenge when Grillby slows, drawing little pleas from Sans. His grip on his fiery wrist tightens again, a silent plea to no, _keep going,_ and Sans even finds that he’s trying to jerk himself off with Grillby’s hand. He’s slow, but he doesn’t stop, like every staggered breath is something Grillby cherishes and wants drawn out of him bit by agonising bit.

“Please,” Sans whispers. He’s never begged like this before. “Keep going-”

The gratified noise Grillby makes sends a shockwave throughout Sans’ body, or maybe it’s because he smears the precome along the tip of Sans’ cock, slow and sweet. It’s torturous, heady and electrifying all at once as Sans attempts to chase that pleasure.

Grillby bends up and kisses him a little roughly. Sans blearily thinks he hears another soft tutt, then the soft sear of fire against sweaty bones. He groans, trying to move forward, to grind his hips forward for more delicious friction and to rub his coccyx against Grillby’s crotch. As always, when he’s denied, Sans’ soul tries to do his work for him. Despite the flames’ visit, they left that part of him alone to burble and weep.

Grillby’s breaths match his own, something Sans didn’t quite figure out until he allowed himself to look. The fire monster is lit up in bright hues, twists of gold and rosy magentas that flicker into cyan flecks. Grillby’s pretty when he’s excited, when he’s a little out of control. Sans can’t help but watch him, flushed himself right down to his collarbones.

It eventually comes to him why Grillby appears as desperate for Sans to slow, to really take his time. Better yet is the angle with which Sans moves, the dip of his coccyx nestled against Grillby’s folds, tracing its line and drawing up pleasure for them both. Rather ashamedly, Sans laughs, lets go of Grillby’s wrist and uses the fire monster’s knees as convenient armrests. Then he grinds down, seeking the heady warmth of Grillby’s cunt as he goes.

Grillby rewards him with a surprised shout. He tilts his hips upwards, matching Sans’ rhythm. Sans feels his legs quiver under his arms. The sensation is heady, sending a liquid shot of satisfaction straight to his brain.

The temperature rises as they play. Sans attempts words, but they tangle on his tongue as he leans down to taste Grillby’s kisses again. All he can manage is some forewarning when Grillby hitches his hips up, his flames out of control. The bed might be a little bit on fire. That’s ok, Sans thinks in a haze.

With the new position, Sans coaxes himself to straddle Grillby’s hips again. He keeps close to his neck, nuzzling, trying not to whimper at the loss of Grillby’s warm hand on his cock. Instead, he searches between them, pivoting his hand between Grillby’s sweatpants and abdomen.

It’s really warm. Sans can feel it radiate into his pelvis, soaking it in like solar rays. It lights up every one of his joints as Grillby resituates a leg, parting them for easier access. Sans pushes down, cupping the folds of Grillby’s sex to run his middle finger down his slit. Grillby tenses underneath him, tantamount pleasure huffed in his voice. It’s all fiery cracks and whimpers.

So out of control. Grillby really is so patient with him.

With his other hand, Sans pulls down the sweatpants so his boyfriend doesn’t set fire to anything else. Grillby clumsily kicks a leg either to help with its removal or because Sans is anxious to thrust inside of him, dense slippery heat coating his fingers. Grillby huffs a shout, the fiery expletive somewhat hushed.

Sans grins despite himself. His soul pounds, leaden and hot in his chest. He feels a couple of spatters hit his ribs on the way down, leaving his cock weeping and ignored. As much as he wants Grillby to continue, he can’t tear his eyes away from the fire monster’s chest heaving with every gasp. He crooks the angle of his thrusts just right and Grillby throws his head back, the air crackling with heat.

So wild. So pretty. Grillby really is a star up close, perfect colours Sans dreams of whenever he looks at the night sky on a clear night. The sounds Grillby makes are ethereal and right, a sound buried under the whispers of fire that chant his name.

He hears it now, fingers slickened by arousal. Grillby explained it once upon a time; something about the state of his body imitating various temperatures to manipulate his body and how it accepted other magic. Or something like that. Sans just wants to bury himself in it.

He somehow resists, though his soul is pounding hard. The next outward push of magic against Grillby’s exposed stomach makes his tongue singe like a burn, but it doesn’t hurt, just an all-encompassing intensity that makes a haggard moan rip from Sans’ throat. Grillby echoes it, his voice on the edge of pleasure so hard it could’ve been pain. His walls clench around Sans’ fingers, rhythmic little throbs as Sans feeds him another finger and glides against his clit with his thumb. A little trick Grillby taught him a time or two.

It’s almost enough, Sans can just taste it. His aching arousal gives a sympathy twinge when Grillby comes. The fire monster looks amazing, in bliss as his back arches and his hands find the sheets to grip in a desperate clutch. The fabric threatens to steam in his fists and Sans can smell it burning as it ignites through Grillby’s orgasm, his shout muffled yet louder than he cares to be. It spikes a heady shot straight through Sans’ soul, rendering him dazed and eager to sink into him.

Grillby’s breathing hard as he winds down, watching Sans through a spray of glittering fire. He looks like sparklers, wound up and brilliant. Sans grins a little as he withdraws his hand from Grillby’s pants, bringing his drenched fingers up to his tongue. It’s just a little taste, but the look Grillby sends him, all hot and love-struck… Sans groans when an anticipatory shudder rolls through Grillby’s flames.

He’s been patient. Grillby’s urging as they both work to undress him. It’s sloppy, caught up in each other, wanting to taste and share and breathe everything. Sans can’t help the laugh stuck in his throat when he slinks his hands behind Grillby’s ass and lifts him into his lap, and Grillby nearly bites the corner of his mouth with the display of urgency.

Sans detangles him from his nightshirt and guides him up, Grillby’s long legs drawn around him. As he gets excited, his flames get out of control, whispering eager vulgarities for Sans to hear, making him flushed and hot. He’s nestled between Grillby’s legs, his cock hard as he tests how much the fire monster will give him.

Decidedly, it’s a lot. Maybe it’s Grillby’s forward thinking that he adjusts his size to take him, or maybe because there’s something awfully appealing about being held down by someone bigger than you, but Grillby’s body scales down just a bit. Not enough to be immediately noticeable, but enough that when Sans leans over him, Grillby gives him an eager grin when they’re matched face-to-face with minimal painful bending. Sans can’t help but double down on Grillby’s leg around his hip as he moves forward.

He’s never been big, but Grillby is always eager to coach him. It’s part of their communication of how Sans can please him. Sans will never be used to the way Grillby sighs when he guides his dick against his folds, nor the way he adjusts how he sits to help Sans find the best angle. It always makes Sans’ soul throb when Grillby looks down just before he enters him, mouth agape like the fire monster _has_ to see their joining and wants to see every last inch of Sans disappear inside of him.

Sans takes his time. Call it revenge for all the merciless ways Grillby’s teased him in the past. The first time he sinks in, all sweet and slow, he savours it when Grillby’s breath hitches and he murmurs an encouraging, wordless sound. He knows what Grillby likes - thicker at the base, eased in slow and steady. Sans’ hips quiver as all-encompassing heat surrounds him, unable to muffle an appreciative moan.

God, he missed this. He can practically feel the pulse of Grillby’s magic surround him, echoing dully in his pelvis like they mean to meld together. The heat is almost too much, ensconced in his brain like the very first time. Helplessly, Sans huffs, bowing his head as he fights not to tip over the edge just by it alone.

He adjusts his hips when Grillby relaxes, the soft roll of movement pleasant and sweet. The fire monster takes a hitched breath despite it not being much at all, and Sans glances up, not wanting to miss it. He tries the small motion again and swallows hard when Grillby’s eyes squint and he sucks in another sharp breath.

“Too big?” he shakily asks. Grillby pulses around him, as though testing the width of him. Sans’ back bends, threatening to push in and take all that he’s offered. He quivers, a moan caught in his throat. It’s almost enough to drive him mad.

Grillby hums softly, slowly clawing into the sheets like it’s the sweetest of tortures. His shaky fingertips leave singed marks in the fabric. _“Go on.”_

Sans feels another anticipatory surge in his pelvis and makes sure to gently tip his hips forward, drawing out just a bit. He remembers to let himself touch him as Grillby always invited him to, sliding a finger around where they’re connected. He throbs and flicks his thumb around to Grillby’s clit, giving him a tease as he draws out. Fuck, he can feel it when Grillby tenses, like he means to keep him.

He feels good. Sans sighs, flushing hot when the fire monster releases a quick groan. His whole body compliments the movement like he means to take everything Sans gives him.

It’s enthralling, making Sans’ soul squeeze fondly.

It’s definitely been too long. He can’t believe how starved Grillby seems to be for affection. He wishes that his body would cooperate more often than once in a blue moon, but Sans gives it his all, recalling memories from when Grillby coached him through their first times. He pumps in once, the rolling pleasure hitting him as Grillby hitches himself up to one elbow, just a taste of him reaching for control.

Gently, Sans pushes a hand down on his abdomen and gives another experimental push, just to see Grillby brighten by bare degrees. A ripple flows through Grillby’s body, and he uses his position to push down to meet with Sans’ next thrust.

He thinks he still feels the flames, gently simmering somewhere hidden around his bones. They don’t do anything, just makes him warm, pleasurable beyond a doubt as he moves. Sans huffs, using Grillby’s position to shamelessly hold his legs around him, setting a gradual tempo that has him seeing stars.

His breaths come in uneven gasps, soft nonsensical little noises escaping his parted teeth when he angles himself just right. He’s a little clumsy, but Sans uses his hand to circle Grillby’s clit, slipping in all his essence as the fire monster rocks to meet him.

Grillby gets oddly loud when he’s being fucked, like a lifetime of shy quietness breaks when he’s alone with Sans. His huffs are complete with moans, soft _Oh’s_ and broken hums a symphony of how much Sans makes him fall apart. He even swears sometimes, like it’s all Sans’ fault that he says such things.

And it is. Sans groans, pleasure rippling through him in waves. He’s not sure whether the flames in his pelvis nestle in close to his foramen, but the sudden burst of pleasure is heady like a shot of liquor. Sans flinches, jerks forward with a shout, grasping at Grillby’s hip like it’ll save him. Driven into with such force, he hears the slippery squelch of Grillby’s pussy.

He shudders. It’s not enough to make him come, but Sans can’t think straight. He wonders, idly, if Grillby did that on purpose, but he looks as wrecked as he does when he drapes an arm over his face. Sans gazes down at him, a little worried that he might’ve hurt him. Sans shudders out a breath, an intense throb somewhere in the back of his hips that coaxes him to do that again. He resists.

“Y.. you ok?” he huffs, and Grillby’s mouth curls into a grin.

Oh. Hello, devil.

 _“…eep going, mnh-”_ Grillby purrs, and Sans can feel it travel down his spine like warm fingertips. _“More.”_

Sans’s grin is crooked. It isn’t in his repertoire to get fast and rough like Grillby does with him, but he supposes he can handle it this time. Especially with the way his hips are coaxed to move, small flames pushing him, tracing around his sacrum to play him like some kind of perverted wind instrument.

He lets it happen again, the deep throb jerking through him when the flame goes deeper, ethereal in its touch yet enough to push him to thrust again. His hips hit Grillby where they’re connected. Grillby’s groan is startled and a little higher than his usual register.

He’s pushed to do it again, and the fires around him brighten. Sans can feel it in his face, warmed by the sun peeking in the window to voyeur their amorous activities. He groans when Grillby nods quickly, holding his breath when he withdraws, only to huff it out on a moan when Sans’ hips snap back.

The rush is addictive, every moment cultivated for Sans to sear into his memory. Grillby clutching at the sheets, the sensation in his body that has him thrusting into him faster, harder, making him adjust their position so he can keep balance. Sans sweats even without the heat, watching with hooded eyes as Grillby’s mouth forms a swear, burnt out on his tongue. It’s hard to pound into him from this angle with only one hand free, so Sans lets up from his clit and holds his hips.

This angle is sweet. Sans feels like he has a lot more energy, like every day past three months gave him something to save away. Grillby is with him, alive and warm, a light in his life, a love in his soul. He feels pent up, unleashed yet under control. Grillby makes him feel this way, and Sans would have it no other way.

The sensual heat locked in his pelvis starts to coil up, tightening the further he pushes into Grillby. He feels it in his bones, right down to the marrow. They’d made headway - or rather, Grillby’s had to grab onto the rails of the headboard in order not to be inched into the wall. His gasps fill the room, that autumnal heatwave trapped in their room as pleasure builds up between the two of them.

Sans whimpers, slowing his thrusts when it starts to feel like it’s too much. He teeters, trapped in a loop as the swirling flames that lick at his coccyx force him forward and the dual sensation of his cock sliding in Grillby’s inner walls overwhelms him. He groans fully, just generously rubbing now as he tries to catch his breath. There’s only so far adrenaline can take him.

All too knowing, Grillby unhooks one of his hands from a railing and leans up, still on Sans’ cock. He does move a bit, giving a soft moan when Sans helplessly hitches up. Sans is simultaneously stuck between nirvana and agony. Still, he’s urged to move his hips even as Grillby attempts to change their position.

 _“Alright..?”_ the fire monster murmurs. It’s heavy and warm like the cosiest of blankets, light touch comforting in its own right. Grillby manoeuvres himself up, gently clasping one of Sans’ hands to he can he pulled up. Almost automatically, Sans helps him. Grillby’s entire body trembles, and it wrenches a pitiful gasp from Sans’ overworked body. _“Go on, it’s alright,”_ he soothes, all tender pleasure dripping from his tongue.

Sans shudders, looping an arm around Grillby’s waist as he moves over him. He remains sitting, urged to cross a leg for balance. Grillby hums low in his throat, pushing into Sans as he captures a kiss. Sans sighs against him as things wind down, sensation rippling over him in waning waves. Shakily, he nods that he’s ok. A little overwhelmed in the moment, but good.

 _“Can you give me words?”_ Grillby asks softly. There’s a hint of a smile behind his flames and it reaches his eyes, pleased by how wrecked he had gotten hidden behind his glasses.

Sans nods again, then grins. It’s crooked, like his smile doesn’t fit too right, but he sighs out a chuckle, his hands finding Grillby’s thighs. He glides them down to his knees and up again, just to feel the fire monster hum against him.

“Keep going?” Sans offers, already leaning in for another kiss. He knows better than to apologise for what he thinks is probably a faux pas; communication is key. He’d tell him, but Grillby also knows how to tell him with body language. Grillby drags a finger down his sternum, igniting and wisping away a few beads of sweat. He rolls his hips as Sans’ fingertips trace up back to his thighs, curling between them like wisps of smoke. “It felt really, really,” he slows between each word, hooked on the way Grillby leans forward to capture his mouth in a slow, intoxicating kiss, “really good.”

When Grillby got up, he had slipped out, achy and needy. He feels Grillby adjust their position, his cock settling on his thigh. Sans hums, wanting nothing more than to press the fire monster against him and sink into him again. He thinks he’s got second wind coming on, drawn in again by Grillby’s addictive kisses.

He’s a little startled by Grillby’s hand on him as he kneels up, lining his cock up to try again. Sans makes an almost pitiful noise, burying it into the fire monster’s shoulder as he starts the slow sink down.

His hands ache where he holds him, steady and shaky at the same time. The new angle has affection roiling up in Sans’ chest, with Grillby so close he can feel the thrum of his own soul. It’s more tender now, caressing Grillby as he stakes his claim on him. Sans nearly shudders again when he can feel the fire monster taste the side of his neck.

He loves him. God, he loves how he moves. Sans is drunk on sensation, moving in a slow haze of soul beats and tender kisses. He loves how his back aches, how Grillby slowly grinds against him, barely moving yet taking all of him at once. The flames recede, and there’s only a bubble of pleasure, growing and growing until it eventually pops.

It’s a slow eruption. Grillby treats him well, wanton shivers rolling over Sans as waves of pleasure lap at him. He holds on, accepting kisses like favours, gently returning them as Grillby sighs into his mouth with each careful thrust. Grillby wants him. Grillby _needs_ him, as intoxicating as that thought is.

Sans curls his arm under the fire monster’s, holding him close as his breaths pick up. He thinks he’s close. If the soft shuddering noises Grillby’s making have anything to do with it, so is he. The kisses drop away, eventually seeking closer comfort within each others’ arms. Sans can’t hold back the whimper when it comes to be too much.

Grillby’s the first to come. Sans can tell by the constricting pulses around his cock, sending him so close he muffles a grunt against Grillby’s fiery shoulder. He tries so hard not to bite down, only grazing his teeth against the cragg-like form beneath the flames. Grillby gives a higher shout as he does so, riding him through his orgasm.

When the speckles of white clear from Sans’ vision, he’s still holding onto Grillby, leaning into him fully. He’s still buried within him, still soaking up his warmth like he’ll freeze if Sans ever let him go. His breaths burn as he listens to the drum of Grillby’s soul heavy in his skull, tattooing a song he never wants to fall silent.

Grillby’s kisses are soft and soothing. His hands warm. His body bright, seeking out all the dark spaces in Sans’. He feels tender, right in ways that Sans just can’t put a name to. It’s rare that he feels so complete, but with Grillby, Sans feels like he could want for nothing else.

He lifts his head from Grillby’s shoulder and nestles him close, both arms wrapped around the fire monster’s body. He widens his lap a little, but Grillby stays put with a muted grunt of protest like he wants to keep him a bit longer.

Their bodies wind down, beating as one, so drunk off each other that it’s probably another hour before Sans starts to feel the euphoria melt away. He protests despite himself, gently patting Grillby’s arm wrapped around behind his skull. He gets clingy. That’s ok. Sans likes to feel wanted.

He pushes their mouths together, a gentle brush of teeth and fire. Grillby’s dozy. It’s probably a first that Sans hasn’t just conked out before he did. Sans lazily grins despite himself, teetering like he’s threatening to pull him down into the burnt sheets. Eventually, Grillby lets his arm slide from Sans’ shoulder so he can be guided down. In his current state, he shines brighter than the perverted sun shining through the slatted blinds.

Drowned in warmth, Sans joins Grillby in comfort and relaxes beside him, drawing him near. The regular aches catch up with him, but he watches as the fire monster tucks in close, curling fingers under his jaw for safe-keeping. Sans pushes his body one last time and inches closer, depositing another kiss against the side of Grillby’s neck where he had marked up before.

After all, he loves him.

**Author's Note:**

> If you liked this fic, please let me know ♥ I thrive on comments!!! :D


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